Low-temperature continuous process to derive size-controlled lithium ion anodes and cathodes

ABSTRACT

The disclosure relates to a process to synthesize nanostructures of a uniform size distribution and/or morphology, nanostructures resulting therefrom, and the use of the nanostructures in energy storage devices.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 61/731,771, filed Nov. 30, 2012, the disclosure of which isincorporated herein by reference.

TECHNICAL FIELD

The invention relates to methods to synthesize nanostructures, such aslithium metal phosphate nanoparticles, and the use thereof in energystorage devices, such as Li-insertion batteries.

BACKGROUND

Methods to make nanoparticles for energy storage devices, such aslithium metal phosphates, use solid-state reactions at high temperaturesresulting in nanoparticles that are heterogeneous in size andmorphology. These methods, therefore, have to incorporate an additionalmilling or grinding step in attempts to reduce and make more uniform thenanoparticle size distribution. Non-uniform nanoparticle size andmorphology increases stress concentrations and de-stabilizes chargedistribution in energy storage devices.

SUMMARY

The disclosure provides a method of synthesizing size and/ormorphologically controlled nanostructures comprising depositing areaction mixture comprising a first metal salt and a second metal saltonto a substrate, wherein the substrate is heated to room temperature orgreater for at least 30 seconds, depending upon the temperature and thedesired crystal size, under conditions for nucleation and growth ofnanostructures on the substrate.

A method of synthesizing size and/or morphologically controllednanostructures comprising depositing a reaction mixture comprising afirst metal salt and a second metal salt onto a substrate, wherein thesubstrate is heated to room temperature or greater for at least 2seconds under conditions for nucleation and growth of nanostructures onthe substrate. In one embodiment, the reaction mixture is sprayed ontothe substrates. In another embodiment, the reaction mixture is formed bymixing a solution comprising a first metal salt with a solutioncomprising a second metal salt. In yet another embodiment, the methodfurther comprises adjusting the pH of the solution comprising the firstmetal salt by adding either an acid or base, adjusting the pH of thesolution comprising the second metal salt by adding either an acid orbase and/or adjusting the pH of the reaction mixture by adding either anacid or base. In yet another embodiment, the method further comprisesadding one or more specific polymers to the solution comprising thefirst metal salt, adding one or more specific polymers to the solutioncomprising the second metal salt and/or adding one or more specificpolymers to the reaction mixture. In yet another embodiment, the firstmetal salt comprises a transition metal. In a further embodiment, thetransition metal selected from the group consisting of manganese, iron,titanium, zinc, copper, cobalt and nickel. In a specific embodiment, thetransition metal is iron. In yet another embodiment, the first metalsalt comprises a polyatomic anion. In yet a further embodiment, thepolyatomic anion is selected from the group consisting of phosphate,sulfate, nitrate, molybdate, oxalates, chlorate, and carbonate. In aspecific embodiment, the polyatomic anion is sulfate. In anotherembodiment, the first metal salt is dissolved in one or more polarsolvents. In a further embodiment, the first metal salt is dissolved inwater and/or a glycol. In a further embodiment, the first metal salt isdissolved in a mixture of water and triethylene glycol. In anotherembodiment, the second metal salt comprises lithium. In anotherembodiment, the second metal salt comprises a polyatomic anion. In afurther embodiment, the polyatomic anion is selected from the groupconsisting of hydroxide, perchlorate, carbonate, diethyl carbonate,tetrafluoroborate, hexaflourophosphate, and triflate. In yet a furtherembodiment, the polyatomic anion is hydroxide. In another embodiment,the second metal salt is dissolved in one or more polar solvents. In yeta further embodiment, the second metal salt is dissolved in water and/ora glycol. In yet a further embodiment, the second metal salt isdissolved in triethylene glycol. In another embodiment, theconcentration of the first metal salt is equal to the concentration ofthe second metal salt. In another embodiment, the concentration of thefirst metal salt is greater than the concentration of the second metalsalt. In yet another embodiment, the concentration of the first metalsalt is less than the concentration of the second metal salt. In anotherembodiment, the concentration of the first metal salt is at least threetimes less than the concentration of the second metal salt. In anotherembodiment, the pH of the solution comprising the first metal salt, thepH of the solution of comprising the second metal salt, and/or the pH ofthe reaction mixture, is adjusted with either nonaqueous or aqueousacid. In a further embodiment, the pH of the solution comprising thefirst metal salt is adjusted with nonaqueous polyprotic acid. In stillyet a further embodiment, the nonaqueous polyprotic acid is phosphoricacid. In further embodiment, the pH of the reaction mixture is adjustedwith aqueous polyprotic acid. In yet a further embodiment, the aqueouspolyprotic acid is aqueous sulfuric acid. In another embodiment, thesubstrate is heated at room temperature or greater for at least 30seconds. In a further embodiment, the substrate is heated at 50° C. orgreater for at least 30 seconds. In yet a further embodiment, thesubstrate is heated at 100° C. or greater. In still yet a furtherembodiment, the substrate is heated at 150° C. or greater for at least30 seconds. In yet a further embodiment, the substrate is heated at atemperature between 150° C. to 200° C. for 30 seconds to 12 hours. Inanother embodiment, the method produces nanostructures that have auniform size distribution on the substrate. In a further embodiment, thenanostructures have diameters of less than 100 nm. In anotherembodiment, the method produces nanostructures deposited on thesubstrate, wherein the nanostructure have a uniform morphology. In yet afurther embodiment, the morphology is selected from the group consistingof nanoparticles, nanobelts, nanocubes, and nanoprisms.

The disclosure also provides an energy storing device comprisingnanostructures made by the methods described herein. In one embodiment,the energy storing device is a Li-insertion battery.

BRIEF DESCRIPTION OF FIGURES

The accompanying Figures, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thedisclosure and, together with the detailed description, serve to explainthe principles and implementations of the disclosure.

FIG. 1 shows a general apparatus and system of the disclosure.

DETAILED DESCRIPTION

As used herein and in the appended claims, the singular forms “a,”“and,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a nanostructure”includes a plurality of such nanostructures and reference to “thenanostructures” includes reference to nanostructures resulting from theprocess and reaction conditions disclosed herein.

Also, the use of “or” means “and/or” unless stated otherwise. Similarly,“comprise,” “comprises,” “comprising” “include,” “includes,” and“including” are interchangeable and not intended to be limiting.

It is to be further understood that where descriptions of variousembodiments use the term “comprising,” those skilled in the art wouldunderstand that in some specific instances, an embodiment can bealternatively described using language “consisting essentially of” or“consisting of.”

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this disclosure belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice of the disclosed methods and compositions, the exemplarymethods, devices and materials are described herein.

Materials used to make cathodes for lithium insertion batteries compriselarge particles that lack homogeneity in size distribution. Currentmethods to synthesize LiFePO₄ particles use solid-state reactions athigh temperatures, co-precipitation in aqueous media, hydrothermalsynthesis or mechanical-chemical activation. The resulting LiFePO₄particles range in size from the 100's of nanometers in diameter to the100's of microns in diameter. Such heterogeneity in particle size causesstress to be focused in limited areas, resulting in degrading themechanical properties of the materials during charge and discharge. Theconcentration of stress is due to the difference in strain withinparticles that are partially charged (i.e., particles that are partiallyfilled with Li-ions). Continuous charging and discharging can causemechanical strain that leads to cracking and eventual failure ofcathodes. In addition, the large sizes of cathode particles can lead toextreme charging times and makes the battery use impractical. Usingsmaller particles can avoid this long charge time, but have lower tapdensities (fill densities) that reduce energy density.

The process disclosed herein controls the deposition size and/or shapeof the deposited crystals in a facile one-step and continuous process.Traditional lithium-iron phosphate (LFP) materials are synthesized insolid-state reactions at high temperatures, and require co-precipitationin aqueous media, hydrothermal synthesis or mechanical-chemicalactivation. Since the process disclosed herein is carried out underrelatively mild conditions, there is no need for costly capitalequipment, waste disposal, and/or labor costs (from time intensiveprocessing).

The method to make nanostructures disclosed herein comprises applying areaction mixture to a heated substrate. The method comprises preparing asolution comprising a first metal salt with a solution comprising asecond metal salt. The method may further comprise one or more pHadjustment steps, polymer addition steps, and/or purification steps. Themethod disclosed herein, involves dissolving a first metal salt in asolvent, dissolving a second metal salt, combining the dissolved metalsalts to form a reaction mixture, and then applying the reaction mixtureof a substrates at room temperature or greater and allowing the appliedmixture to incubate on the substrates for a sufficient period of time(e.g., from about 2 seconds to several hours; from about 2 seconds to 48hours, 2-24 hours, 2-10 hours, 5-10 hours, 2-4 hours and any range ornumerical value of any of the foregoing). The method disclosed herein,may further comprise steps to adjust the pH of the solutions, steps toadd polymers to the solutions or reaction mixture and/or add steps forpurifying the resulting nanoparticles. Choice of the solvent/co-solventsystems, addition of specific polymers, and modifying the pH of thesolutions, enables size and morphological control of the resultingnanostructures. Using the method disclosed herein, one can obtainlithium-iron phosphate nanocrystals with a controlled range of size andshapes disposed on a substrate. Advantages of the method disclosedherein include, but are not limited to: (i) precise control of the shapeand/or size of the deposited nanostructures, (ii) the nanostructuresproduced can be used in battery cathodes, e.g., batteries with a needfor fast charge times and potential for high tap densities, (iii) it isa relatively inexpensive method, and (iv) it can be easily scaled up forindustrial production based on the potential for continuous processing.

The size and/or shape of the crystals can be controlled through thesynthesis and deposition process disclosed herein comprising dissolvinga first metal salt in one or more solvents. In a particular embodiment,the first metal salt comprises a metal that is an alkali metal, alkalineearth metal, transition metal, post-transition metal, or lanthanide. Ina further embodiment, the first metal salt comprises a metal that is atransition metal. In a yet further embodiment, the first metal saltcomprises a metal selected from the group comprising, manganese, iron,titanium, zinc, copper, cobalt and nickel. In a certain embodiment thefirst metal salt comprises iron.

In another embodiment, the first metal salt comprises either apolyatomic anion or monoatomic anion. In a further embodiment, the firstmetal salt comprises a polyatomic anion and/or monoatomic anion selectedfrom the group comprising sulfate, nitrate, phosphate, halide,dihydrogen phosphate, acetate, hydrogen sulfite, hydrogen sulfate,hydrogen carbonate, nitrite, cyanide, hydroxide, permanganate,hypochlorite, chlorate, perchlorate, hydrogen phosphate, oxalate,sulfite, carbonate, chromate, dichromate, silicate, molybdate,phosphite, diethyl carbonate, tetrafluoroborate, hexaflourophosphate,and triflate. In yet another embodiment the first metal salt comprises apolyatomic anion selected from the group comprising phosphate, sulfate,nitrate, molybdate, oxalate, chlorate, and carbonate. In a certainembodiment the first metal salt comprises a polyatomic anion that iseither sulfate, or phosphate. In yet another embodiment the first metalsalt comprises a polyatomic anion that is a sulfate.

In a particular embodiment, the first metal salt is dissolved in one ormore solvents. In another embodiment, the first metal salt is dissolvedin one or more polar solvents. In a further embodiment, the first metalsalt is dissolved in one or more aqueous and/or non-aqueous solvents. Ina further embodiment, the first metal salt is dissolved in one or morepolar solvents comprising water, dihydroxy alcohols, alcohols, aceticacid, formic acid, ethyl acetate, tetrahydrofuran, dichloromethane,acetone, acetonitrile, dimethylformamide, dimethyl sulfoxide, and thelike. In a further embodiment, the first metal salt is dissolved inmixture of solvents. In yet a further embodiment, the first metal saltis dissolved in water and/or a glycol, such as triethylene glycol (TEG).In a certain embodiment, the first metal salt is dissolved in water andTEG, wherein this water/TEG mixture can range from almost 99.9% water toalmost 99.9% TEG with specific volumetric ratios in between depending ondesired product.

The size and/or morphology controlled nanostructure synthesis processdisclosed herein comprises forming a reaction mixture comprisingcombining a solution comprising a first metal salt with a solutioncomprising a second metal salt.

In a certain embodiment, the second metal salt comprises a metal that isan alkali metal, alkaline earth metal, transition metal, post-transitionmetal, or lanthanide. In a further embodiment, the second metal saltcomprises a metal that is an alkali metal. In a certain embodiment, thesecond metal salt comprises lithium.

In another embodiment, the second metal salt comprises either apolyatomic anion or monoatomic anion. In a further embodiment, thesecond metal salt comprises a polyatomic anion and/or monoatomic anionselected from the group comprising sulfate, nitrate, phosphate, halide,dihydrogen phosphate, acetate, hydrogen sulfite, hydrogen sulfate,hydrogen carbonate, nitrite, cyanide, hydroxide, permanganate,hypochlorite, chlorate, perchlorate, hydrogen phosphate, oxalate,sulfite, carbonate, chromate, dichromate, silicate, molybdate,phosphite, diethyl carbonate, tetrafluoroborate, hexaflourophosphate,and triflate. In another embodiment, the second metal salt compriseshydroxide, perchlorate, carbonate, diethyl carbonate, tetrafluoroborate,hexaflourophosphate, or triflate. In yet another embodiment the secondmetal salt comprises a polyatomic anion that is hydroxide.

In a particular embodiment, the second metal salt is dissolved in one ormore solvents. In another embodiment, the second metal salt is dissolvedin one or more polar solvents. In a further embodiment, the second metalsalt is dissolved in one or more aqueous and/or non-aqueous solvents. Ina further embodiment, the second metal salt is dissolved in one or morepolar solvents comprising water, dihydroxy alcohols, alcohols, aceticacid, formic acid, ethyl acetate, tetrahydrofuran, dichloromethane,acetone, acetonitrile, dimethylformamide, dimethyl sulfoxide, and thelike. In a further embodiment, the second metal salt is dissolved inmixture of solvents. In yet a further embodiment, the second metal saltis dissolved in water and/or a glycol, such as triethylene glycol (TEG).In a certain embodiment, the second metal salt is dissolved in water andTEG, wherein this water/TEG mixture can range from almost 99.9% water toalmost 99.9% TEG with specific volumetric ratios in between depending ondesired product.

The ratio of the concentrations of the first metal salt with that of thesecond metal salt will primarily dictate the relative size of thenanostructures disclosed herein, wherein the higher the concentration ofthe first metal salt as it relates to the second metal salt, the smallerthe resulting nanostructures. In a particular embodiment, theconcentration of the first metal salt is equal to concentration to thesecond metal salt. In another embodiment, the second metal salt is at agreater concentration than the first metal salt. In a yet furtherembodiment, the concentration of the second metal salt is at least twicethe concentration of the first metal salt. In a yet further embodiment,the concentration of the second metal salt is at least three times theconcentration of the first metal salt. In a yet further embodiment, theconcentration of the second metal salt is between two times to ten timesthe concentration of the first metal salt. In another embodiment, theconcentration of the first metal salt is greater than the concentrationof the second metal salt. In a yet further embodiment, the concentrationof the first metal salt is at least two times the concentration of thesecond metal salt. In a yet further embodiment, the concentration of thefirst metal salt is at least three times the concentration of the secondmetal salt. In yet another embodiment, the concentration of the firstmetal salt is between two times to ten times the concentration of thesecond metal salt.

The size and/or morphology controlled nanostructure synthesis processdisclosed herein comprises a heating step/incubation step, wherein areaction mixture is deposited (e.g., sprayed) on a substrate that isheated to between about 25° C. and 400° C., wherein the reaction mixtureis formed by combining a solution comprising a first metal salt with asolution comprising a second metal salt. In instances where the pH ofthe reaction mixture is adjusted and/or where one or more specificpolymers are added to the reaction mixture, shall be interpreted for thepurposes of this section to be included in the term “the reactionmixture.” In a certain embodiment, the reaction mixture is applied atroom temperature and allowed to incubate on a substrate for at least2-24 hours. In a certain embodiment, the reaction mixture is applied atleast 50° C. and allowed to incubate for at least about 2 hours. Inanother embodiment, the reaction mixture is applied at about 100° C. andallowed to incubate for at least about 2 hours. In yet anotherembodiment, the reaction mixture is applied at about 150° C. and allowedto incubate for at least about 2 hours. In a further embodiment, thereaction mixture is applied at about 200° C. and allowed to incubate forat least about 2 hours. In yet a further embodiment, the reactionmixture is applied to a substrate and the substrate is heated (e.g., seeFIG. 1).

Using the method of the disclosure, one can control solution conditions(e.g., ions mixed in an aqueous-based solvent with controlled pH, ionconcentration) to grow anode and cathode materials (such as TiO₂ andLiFePO₄) nanostructures on heated templates (either single crystal,polycrystalline or amorphous). The reaction comprises dissolving theappropriate metal and non-metal salts (such as iron sulfate andphosphoric acid) in a solvent (e.g., water/TEG (triethylene glycol))with H₂SO₄ added to control pH and thus, hydration of cations. Asmentioned above a dopant cation (e.g., Y, Mn, Co, Ni, etc.) can be addedduring the mixing of the Li-ion cathode precursor to ensure the dopantis incorporated within the LiFePO₄. The precursor (and dopants) solutionis then placed in a vessel. A nozzle or other device can be fluidlyconnected to the vessel and is used to control the rate of deposition(e.g., spraying) and the droplet diameter that impinges on thetemplate/substrate. The template can be heated from 25° C.-400° C.(e.g., 80° C.-200° C.). The deposition, such as by spraying, of thisprecursor onto the heated template/substrate enables the nucleation andgrowth on the template/substrate in a controllable manner, producingnanostructures whose crystal size, phase and orientation are dictatedboth by the solution conditions, heating conditions, and the underlyingtemplate/substrate. The resulting product is a solid substrate (e.g., anelectrode) with oriented nanostructures growing from its surface (e.g.,crystalline nanostructures of LiFePO₄) that can be used, for example, inLi-ion batteries. The advantages of this process are that the size,phase and orientation of the nanostructures can be controlled, yieldinghigher efficiency devices. The three advantages are that (i) thereaction can be scaled and used to produce many different metal oxides,nitrides, sulfides, etc. and (ii) the substrate can be chosen as long asit is stable to the temperature at which nucleation and growth occur(e.g., 25° C.-400° C.), (iii) the solution parameters can be modified tocontrol size and phase of crystals growing on this substrate. This couldalso be used for solar-based applications.

In a further embodiment, the size and/or morphology can be controlledthrough the deposition process and through preparation of the reactionmixture. For example, the process disclosed herein can further compriseone or more pH adjustment steps. In a particular embodiment, the pH of asolution comprising a first metal salt, the pH of a solution comprisinga second metal salt and/or the pH of the reaction mixture, is adjustedby adding either an acid or base. In another embodiment, the pH of asolution comprising a first metal salt, the pH of a solution comprisinga second metal salt and/or the pH of the reaction mixture, is adjustedby adding an acid. In a further embodiment, the pH of a solutioncomprising a first metal salt, the pH of a solution comprising a secondmetal salt and/or the pH of the reaction mixture, is adjusted by addinga multiprotic acid. In yet another embodiment, the pH of a solutioncomprising a first metal salt, the pH of a solution comprising a secondmetal salt and/or the pH of the reaction mixture, is adjusted by addingan aqueous acid solution. In a further embodiment, the pH of a solutioncomprising a first metal salt, the pH of a solution comprising a secondmetal salt and/or the pH of the reaction mixture, is adjusted by addinga nonaqueous and/or aqueous multiprotic acid solution including, but notlimited to, phosphoric acid, sulfuric acid, carbonic acid, sulfurousacid, oxalic acid, malonic acid, or hydrogen sulfide acid. In yet afurther embodiment, the pH of a solution comprising a first metal salt,the pH of a solution comprising a second metal salt and/or the pH of thereaction mixture, is adjusted with phosphoric acid. In anotherembodiment, the pH of a solution comprising a first metal salt, the pHof a solution comprising a second metal salt and/or the pH of thereaction mixture, is adjusted with aqueous sulfuric acid.

In a further embodiment, the size and/or morphology can be controlled byuse of one or more polymer addition steps. For example, one or morespecific polymers (e.g., polyvinyl pyrrolidone, polyacrylic acid) can beadded to a solution comprising a first metal salt, a solution comprisinga second metal salt and/or to the reaction mixture. In a particularembodiment, one or more polymers are added to the reaction mixture. Inaddition, the polymer can be modified to one that morphologicallycontrols metals, metal nitrides, metal carbides, etc. The polymer canalso be modified to be electrically conducting, allowing the productionof electronic and optoelectronic devices.

In a certain embodiment, the size and/or morphology can be controlled byone or more purification steps. Examples of purification steps includebut are not limited to, removing solvents by evaporation, removingsolvents by drying, filtering, trituration, extraction, sedimentation,size exclusion chromatography, preparative column chromatography, andthe like.

The size and/or morphology of the nanostructures disclosed herein can becontrolled by varying the water/TEG proportions, as well as, adjustingthe pH of the solutions, adding specific polymers, adjusting the ratioof the metals, and the like. Thus, the properties and characteristics ofthe nanostructures disclosed herein can be tailored by specific reactionconditions. By adjusting such reaction conditions, the nanostructureswill change in size and/or morphology.

In a certain embodiment, using the size and/or morphology controllednanostructure synthesis process disclosed herein results innanostructures that are uniform in size and/or morphology. In anotherembodiment, using the process disclosed herein results in LFPnanostructures that are uniform in size and/or morphology. In yetanother embodiment, using the process disclosed herein results innanostructures that are nanoparticles. In a further embodiment, usingthe process disclosed herein results in nanostructures that arenanoprisms. In yet a further embodiment, using the process disclosedherein results in nanostructures that are nanobelts. In a certainembodiment, using the process disclosed herein results in nanostructuresthat are nanocubes.

In a particular embodiment, using the size and/or morphology controllednanostructure synthesis process disclosed herein results innanoparticles having a near uniform size distribution. In a certainembodiment, using the process disclosed herein results in structuresthat are less than 100 μM in diameter. In yet another embodiment, usingthe process disclosed herein results in structures that are less than 10μM in diameter. In another embodiment, using the process disclosedherein results in nanostructures that are less than 1 μM in diameter. Ina certain embodiment, using the process disclosed herein results innanostructures that are less than 400 nM in diameter. In a furtherembodiment, using the process disclosed herein results in LFPnanostructures that are less than 100 nM in diameter. In yet a furtherembodiment, using the process disclosed herein results in LFPnanostructures that are less than 50 nM in diameter.

In a particular embodiment, a nanostructure disclosed herein is LFPnanoprisms of 1 μm×100 nm. In another embodiment, a nanostructuredisclosed herein is LFP nanoparticles of 25 nm. In yet anotherembodiment, a nanostructure disclosed herein is 100 nm LFP nanocubes. Ina certain embodiment, a nanostructure disclosed herein is 10 μm×400nm×20 nm LFP nanobelts.

In another embodiment, one or more devices comprise one or morenanostructures synthesized using the size and/or morphology controllednanostructure synthesis process disclosed herein. In a furtherembodiment, one or more devices comprising one or more nanostructuressynthesized using the process disclosed herein can be used for energystorage. In yet a further embodiment, one or more devices comprising oneor more nanostructures synthesized using the process disclosed hereincan be used for Li-insertion batteries. In another embodiment, cathodesfor an energy storing device comprise nanostructures synthesized usingthe process disclosed herein.

As described above and elsewhere herein, the concentration of precursorcan vary, from 0.001M-10M, depending on the size and thickness ofLiFePO₄ desired. To make LiFePO₄ nanostructures with this precursor, thetypical concentration is 0.1M-1M. The thickness of the film is alsodetermined by the choice of solvent and template, which can be adjustedto make hydrophilic or hydrophobic conditions. Thus, the properties andcharacteristics of the films can be tailored by the specific reactionconditions. A substrate that is thermally stable to the reactiontemperature and pH can be utilized.

The template/substrate can be single, polycrystalline or amorphous metal(or other substrates) that will facilitate electron collection. In fact,the templates could also be metal oxide contact pads that would serve asboth templates for TiO₂ (or other metal oxide growths) in dye-sensitizedsolar cells and as source and drain in a device. Thus, devices could beconstructed using this method and tested (e.g., resistivity) directlyafter synthesis.

The reaction temperature does not have to be 80° C.-200° C. although attemperatures less than 80° C., amorphous or non-LiFePO₄ phases mayresult. Also, a minimum of −7° C. should be used to enable thesolubility and hydrolysis and condensation of the LiFePO₄-precursor.

The reactor can be scaled to smaller or larger volumes, only limited bythe cost to manufacture these reactors. These reactions are not limitedto LiFePO₄ but can include, for example, TiO₂ and can be modified withmetal nanostructures (Au, Pd, Pt, Ru, Ni, etc.), metal oxidenanostructures (ZnO, Co₃O₄, ZrO₂, RuO₂, SnO₂, Al₂O₃), metal nitride(AlN, BN, GaN, InN), or any combination of inorganic compounds (e.g.,AlON, InGaN). The solvent does not have to be water+TEG and can bevariations thereof. Other non-aqueous based solvents (e.g., alcohols,ethers, etc.) can be utilized to synthesize materials that wouldotherwise not form under aqueous conditions.

The advantages of this process over existing practices are (i) theone-step processing involved (enabling one step device fabrication usingelectrode contacts as substrates for cathode or anode deposition), (ii)the low cost (circumventing the need for costly capital equipment, wastedisposal, and labor costs (from time intensive processing), (iii) thecontrol over size and phase, (iv) control over crystallographicorientation of the grown nanostructures by the underlying template(substrate) used.

FIG. 1 depicts a device/system of the disclosure for coating a substratewith nanostructure of the disclosure. The system 10 comprises a stage 20and temperature element(s) 30. The temperature elements are used toheat/cool the stage to a desired temperature. The temperature element 30can comprise a heat lamp or heating coil or cooling coil or acombination thereof. In some embodiments the temperature element isthermally coupled to the stage 20. The stage 20 can comprise an X-Ystage and may include a motor to move the stage in a Z-direction (notdepicted). The stage 20 serves to support a substrate 40 to be coatedwith nanocrystalline precursor droplets 50. The substrate may be asingle sheet or may be part of a continuous feed system on a conveyorbelt or other continuous feed system 60. A nozzle 70 is located abovethe stage 20 so that during operation precursor droplets 50 emitted fromthe nozzle can impinge on the substrate 40. A reservoir (not depicted)serves to hold the precursor material and is fluidly connected to thenozzle 70.

In operation, the precursor material is mixed as described above anddelivered to the reservoir. An inert air supply system delivers pressureto the reservoir to cause the precursor material to be emitted from thenozzle 70 onto the substrate 40. The substrate can be immobile or may beon a continuous feed system. The precursor droplets 50 are emitted fromthe nozzle 70 at a desired rate to coat the substrate to a desireddensity and/or thickness. In addition, the emission rate also definesthe particle droplet size and is controlled by the delivery rate. Thetemperature element heats the substrate to a desired temperature toallow for nucleation and growth of nanostructures on the substrate.

Using the methods described herein LiFePO₄ tapes can be produced in acontinuous process at reduced temperatures. A spray coating techniquecan be used to continually produce cathode tapes. A precursor solutionsis mixed in the proper concentrations (alternatively, LiFePO₄nanoparticles can be suspended) and injected through a spray nozzleoperated at varied pressures. A current collector (aluminum or coppersheet) is placed on a heated substrate. The spray is directed on theheated current collector, which enables evaporation of solvent andpyrolysis of precursor, which decomposes and crystallizes to form acontinuous thin film of crystalline LiFePO₄.

The following Examples present methods and reactions to synthesize thenanostructures of the disclosure. These Examples are presented asgeneralized guides to make the nanostructures of the disclosure, andshould not be interpreted as the definitive process to make thenanostructures of the disclosure. Moreover, variations in the Examplespresented below, include, but not limited to, the choice of solvent,choice of metal salts, concentrations of the metal salts, changes in theheating step, changes or removal of the pH adjusting agents, changes orremoval of the types and classes of polymers, adding additionalpurification steps, are not only presented as alternatives in thedisclosure but are contemplated as being subsumed in the followingExamples.

EXAMPLES

All of the solutions listed herein were mixed under vigorous stirring(˜500 rpm) and at ambient temperature.

Process to Synthesis Lithium-Iron Phosphate Nanostructures:

Solution 1: A water soluble iron precursor (iron sulfate (FeSO₄.7H₂O,concentration from 0.001M-1M) solution was dissolved in a mixture ofdegassed water and triethylene glycol (TEG), wherein this water/TEGmixture can range from almost 100% water to almost 100% TEG withspecific volumetric ratios in between depending on desired product.

Solution 2: An aqueous solution (concentration was 3 times that of theFe concentration) of LiOH.H₂O was prepared and mixed with TEG.

Solution 3: An equimolar (to iron) solution of H₃PO₄ was then added toSolution 1.

Solution 4: Solution 3 was combined with Solution 2 and the pH wasadjusted to a desired level by adding an aqueous solution of H₂SO₄.

Solution 5: An aqueous solution of a polymer (a variety of polymers canbe selected with a specific pendant group to control size andmorphological features) was mixed with solution 4.

Solution 6: The pH of solution 5 was adjusted to the desired level byadding an aqueous solution of H₂SO₄.

Solution 6 was added to a vessel comprising a nozzle and was ejectedthrough the nozzle onto a template/substrate heated to about 120° C.

In yet another embodiment of the methods, lithium hydroxide is dissolvedin degassed water (final concentration Li=0.3M). This solution is thenadded to an equal volume of triethylene glycol (TEG). To this, 0.1M ofH₃PO₄ is added. A ferrous sulfate powder (final concentration 0.1M) isdissolved in the water+TEG+LiOH+H₃PO₄ solution at room temperature. Thisreaction is stirred for 30 minutes at 700 rpm. Dilute H₂SO₄ can be addedto modify the pH in order to control the shape of LiFePO₄. A singlecrystal, polycrystalline (often, polycrystalline aluminum) or amorphoussubstrate (˜1 cm×1 cm, although any size can be used) is then placed ona heated plate at 120° C. (between 80° C.-200° C.). The precursorsolution is flowed through a pipette, the pipette tip serving as anozzle. The reaction solution is dripped/sprayed onto the heatedsubstrate. The precursor is then allowed to incubate on the substratefor 1-20 minutes (depending on the temperature) and then cooled.

A number of embodiments of the disclosure have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the disclosure.Accordingly, other embodiments are within the scope of the followingclaims.

1. A method of synthesizing size and/or morphologically controllednanostructures comprising depositing a reaction mixture comprising afirst metal salt and comprising a second metal salt onto a substrate,wherein the substrate is heated to room temperature or greater for atleast 2 seconds under conditions for nucleation and growth ofnanostructures on the substrate.
 2. The method of claim 1, wherein thereaction mixture is formed by mixing a solution comprising a first metalsalt with a solution comprising a second metal salt.
 3. The method ofclaim 2, further comprising, adjusting the pH of the solution comprisingthe first metal salt by adding either an acid or base, adjusting the pHof the solution comprising the second metal salt by adding either anacid or base and/or adjusting the pH of the reaction mixture by addingeither an acid or base.
 4. The method of claim 2, further comprising,adding one or more specific polymers to the solution comprising thefirst metal salt, adding one or more specific polymers to the solutioncomprising the second metal salt and/or adding one or more specificpolymers to the reaction mixture.
 5. The method of claim 1, wherein thefirst metal salt comprises a transition metal.
 6. The method of claim 5,wherein the transition metal selected from the group consisting ofmanganese, iron, titanium, zinc, copper, cobalt and nickel.
 7. Themethod of claim 6, wherein the transition metal is iron.
 8. The methodof claim 1, wherein the first metal salt and second metal salt comprisea polyatomic anion.
 9. The method of claim 8, wherein the polyatomicanion for the first metal salt is selected from the group consisting ofphosphate, sulfate, nitrate, molybdate, oxalates, chlorate, andcarbonate.
 10. The method of claim 9, wherein the polyatomic anion issulfate.
 11. The method of claim 2, wherein the first metal salt andsecond metal salt are dissolved in one or more polar solvents.
 12. Themethod of claim 11, wherein the first metal salt and second metal saltare dissolved in water and/or a glycol.
 13. The method of claim 12,wherein the first metal salt and second metal salt are dissolved in amixture of water and triethylene glycol.
 14. The method of claim 1,wherein the second metal salt comprises lithium.
 15. (canceled)
 16. Themethod of claim 8, wherein the polyatomic anion for the second metalsalt is selected from the group consisting of hydroxide, perchlorate,carbonate, diethyl carbonate, tetrafluoroborate, hexaflourophosphate,and triflate.
 17. The method of claim 16, wherein the polyatomic anionis hydroxide. 18-20. (canceled)
 21. The method of claim 1, wherein (a)the concentration of the first metal salt is equal to the concentrationof the second metal salt; (b) the concentration of the first metal saltis greater than the concentration of the second metal salt; or (c) theconcentration of the first metal salt is less than the concentration ofthe second metal salt. 22-24. (canceled)
 25. The method of claim 3,wherein the pH of the solution comprising the first metal salt, the pHof the solution of comprising the second metal salt, and/or the pH ofthe reaction mixture, is adjusted with either nonaqueous or aqueousacid.
 26. The method of claim 25, wherein the pH of the solutioncomprising the first metal salt is adjusted with nonaqueous polyproticacid.
 27. The method of claim 26, wherein the nonaqueous polyprotic acidis phosphoric acid.
 28. The method of claim 25, wherein the pH of thereaction mixture is adjusted with aqueous polyprotic acid.
 29. Themethod of claim 28, wherein the aqueous polyprotic acid is aqueoussulfuric acid.
 30. The method of claim 1, wherein the substrate isheated at room temperature or greater for at least 30 seconds. 31-33.(canceled)
 34. The method of claim 30, wherein the substrate is heatedat a temperature between 150° C. to 200° C. for 30 seconds to 12 hours.35. The method of claim 1, wherein the method produces nanostructuresthat have a uniform size distribution and/or uniform morphology on thesubstrate.
 36. The method of claim 35, wherein the nanostructures havediameters of less than 100 nm.
 37. (canceled)
 38. The method of claim35, where the morphology is selected from the group consisting ofnanoparticles, nanobelts, nanocubes, and nanoprisms.
 39. An energystoring device comprising nanostructures made by the method of claim 1.40. The energy storing device of claim 39, wherein the energy storingdevice is a Li-insertion battery.